Methods have been developed that utilize dynamic light scattering techniques to probe the mechanical rigidity and internal viscosity of polymer gels. Recent empahsis has been on characterizing changes in mechanical properties that occur near the gel-sol transition, as crosslink density and polymer concentrations are varied. The influence of solvent visocity on the dissipation of mechanical excitation is also being lassessed, to facilitate the formulation of a mathematical model to explain the dependence of measured macroscopic parameters on micorscopic gel structure. Polyacrylamide gels have been used as model networks in these investigations, in part because of the technological materials that have been studied by these techniques recently have included gels formed from glycoproteins obtained from sputum and clots formed from reconstituted human plasma (cf. project Z01 CT 00017-10 PSL). Other activities mainly have involved obtaining information on particle size distributions needed by other investigators at NIH.